15min:

WEI-LI LI, TIAN JIAN, GARY V. LOPEZ AND LAI-SHENG WANG, Brown University, Chemistry Department, 324 Brook St, Providence, RI, 02912.

The uranium fluoride anions (UF_x^-, x=2 - 4) are produced by laser vaporization and investigated using photoelectron spectroscopy at four different photon energies. An extensive vibrational progression of 620 cm^-1 is observed in the spectra of UF₄^-, indicating significant geometry change between the anion and the neutral ground states. Franck-Condon simulation is performed to identify the vertical detachment and the 0-0 transition to get the electron affinity of the neutral UF₄. Preliminary ab initio calculation shows that the U 5f orbitals participate in the bonding with F 2p orbitals. The UF₃^- molecule has multiple vibrational modes active upon electron detachment, yielding congested photoelectron spectra. Two vibrational progressions are observed in the UF₂^- spectra at 580 cm^-1 and 160 cm^-1.